Prior art resistive elements are known which combine deposited resistive material with deposited conductors which form the electrical leads of the resistor. A precise value of resistance is obtained by scribing a line into the resistive material thereby altering the characteristics of the material between the two leads.
One such structure is disclosed in U.S. Pat. No. 4,647,899 assigned to the assignee of the present invention. In that structure, first and second spaced-apart conductive members are joined by a layer of resistive material. The value of the resistor is determined by a laser scribing process. The resistor structure disclosed in that patent has a relatively complex shape.
In another known resistor structure, a generally rectangular, deposited, resistive layer is terminated at each end by deposited conductive layers. Hence, there exists a non-zero resistance between the two conductive layers.
One or more laser cuts are made in the resistive layer so as to trim the resistor to a predetermined value, that is higher than its initial untrimmed value. A single laser scribed line can be used. Alternately, a plurality of spaced-apart laser scribed lines can be used.
Another known form of such a resistor is known as a "top hat" resistor. It has a shape generally corresponding to the cross-section of a top hat.
In such a resistor, prior to any laser scribing of the resistive material there exists a base resistor value due to the resistive material between the two conductive members which form the contacts for the resistor. As the scribing operation proceeds, and the continuity of the resistive material is interrupted, the value of the resistive element increases from the initial base value.
The initial base value is determined by the configuration of the resistor as well as the resistive characteristic of the deposited material, in ohms per square, as well as the physical spacing between the two conductive elements which is filled with the resistive material.
Thick film deposited resistive elements have heretofore not been available in sizes achievable with thin film technology. One of the limitations of prior art thick film deposition technology has been the amount of space which must be maintained between elements so as to insure electrical separation from one another.
For example, known methods of printing thick film resistors and conductors depend on an ability to print specific line widths and spacings of the conductive and the resistive elements. Typically, 10 mil wide lines and 10 mil spacings between elements are achievable in high production environments.
In some instances, with difficulty, it is possible to get down to the 6-7 mil range. However, this size reduction usually results in lower processing speeds with additional inspection steps needed. Problems encountered at this size include insuring line integrity and insuring that there are no line-to-line shorts. Thus, thick film-type technology has been limited by an inability to achieve better and more reliable lines and spaces therebetween.
It would be desirable therefore to be able to form precision electrical components using relatively inexpensive, available thick film deposition technology with sizes approaching sizes which can be achieved using much more expensive thin film technology. In addition, it would be desirable to be able to form dense, precision resistive elements using relatively imprecise thick film deposition techniques for depositing resistive and conductive layers.